Prostate-Specific Antigen Flare Phenomenon Induced by Abiraterone Acetate in Chemotherapy-Naive Patients With Metastatic Castration-Resistant Prostate Cancer.

Abstract Background Prostate-specific antigen (PSA) flare is a well-known phenomenon in patients with prostate cancer treated with luteinizing hormone-releasing hormone agonist and chemotherapy. However, its incidence and the significance for the clinical outcomes of patients treated with abiraterone acetate (AA) are uncertain. Patients and Methods A multicenter retrospective analysis of chemotherapy-naive patients treated with AA for metastatic castration-resistant prostate cancer (mCRPC) was conducted. The baseline characteristics, treatment history of mCRPC, and serum PSA kinetics during AA treatment were collected. The log-rank test was applied to compare progression-free survival (PFS) between patient groups with a PSA flare according to the different definitions and immediate PSA declines. Results The data from 83 patients were analyzed. An immediate PSA decline of any amount was observed in 59 patients (71.1%). According to the various definitions of PSA flare, its incidence ranged from 6.0% to 10.8%. Although the median interval to the peak PSA level was 0.95 month, regardless of the PSA flare definition, the interval to the PSA nadir showed a wide range of 2.8 to 7.6 months. In PSA flare subgroup, the median PFS in patients with any PSA decline to less than the baseline and > 30% decline from the baseline was 12.4 months. The PFS duration of PSA flare patients did not significantly differ from that of patients with an immediate PSA decline of any amount and immediate > 30% decline without PSA flare. Conclusion The PSA flare phenomenon is not rare event during AA treatment. A PSA decline during AA treatment, with or without a PSA flare, was associated with favorable clinical outcomes. Thus, AA should not be withdrawn early in patients with mCRPC in whom an initial, isolated PSA increase has been observed.